Poe U.S. Pat. No. 3,936,898 discloses a "Portable Ramp for Wheelchairs" in which two side plates are joined at the center by a piano hinge so that the ramp can be folded about its longitudinal center line for portability. Each side plate is reinforced by bottom tubular braces. The ramp can be latched in folded condition, and a handle projects from one of the side plates for carrying the folded ramp. Hooks are provided for hanging the folded ramp from the frame of a wheelchair. The Poe construction is appropriate for only a very short ramp, if it is to be truly portable. For example, the Poe ramp might be appropriate for bridging a single low curb or step, but not for a high curb or several steps. Otherwise, the angle of inclination of the short ramp would be greater than desirable. In addition, the Poe ramp would not be appropriate for use with a three-wheeled motor scooter which has a steerable nose wheel in the center because the nose wheel would run over the central hinge.
Packer U.S. Pat. No. 4,528,711 discloses another type of "Portable Wheel Chair Ramp" in which two laterally spaced tracks have narrow channels for the wheels of a wheelchair. Each track is of telescoping construction so that the length of the track can be adjusted. The Packer construction is not appropriate for a three-wheeled motor scooter because there is no central support for the nose wheel.
Another known portable ramp construction uses side rails similar to the tracks of the Packer ramp, but without the inner upright flanges of the channels. Separate rigid panels can be interfitted with the tracks to form a full width ramp appropriate for motor scooters in addition to wheelchairs. Such a ramp is sold under the trademark EZ-ACCESS R3000 SCOOTER RAMP by Homecare Products, Inc. of Kent, Wash., primarily for use as a knock-down loading ramp for vans. The central panels are quite bulky and can be difficult to interlock with the telescoping side rails.